1. Field of the Invention
The present invention relates to a color photographic process for a silver iodobromide (containing at least about 2 mole percent silver iodide) color photographic material and, more particularly, it relates to a color photographic process of performing color intensification (the intensification of dye image densities) in the presence of a cobalt (III) complex at high temperatures of about 50.degree. C or higher.
2. Brief Description of the Prior Art
A color photographic material generally contains from about 1 g to about 15 g of silver halide per square meter of the photographic material. For example, a photographic color negative film or a photographic color reversal film ordinarily contains about 3 to 9 g of silver halide per square meter of the photographic film. Silver or silver halide used in the color photographic film is inevitably consumed in obtaining desirable dye image densities but if it is possible to reduce the amount of silver or silver halide used in the color photographic material without reducing the photographic properties of the photographic material, conservation of silver resources and a reduction in the costs of color photographic materials as well as the costs for processing them can be obtained, which enables commercial photographic products having high quality at a comparatively low cost to be provided.
Therefore, several attempts have been proposed for reducing the amount of silver to be used. A typical example of such an attempt is an intensification of the color images using a peroxide such as hydrogen peroxide as disclosed in U.S. Pat. No. 3,674,490 and a metal complex such as a cobalt (III) complex as disclosed in U.S. Pat. Nos. 3,856,524 (corresponding to Japanese Patent Application (OPI) No. 9728/1973), 3,765,891 and 3,748,138.
However, various difficulties are encountered in the intensification of color images using a peroxide such as hydrogen peroxide. First, a peroxide is very unstable in an aqueous solution. Second, when the period of time required for the intensification is prolonged, the dye images formed are damaged. Third, the performance of the intensification is accompanied by the formation of a large amount of fogging.
On the other hand, the intensification using a metal complex is superior to the intensification using a peroxide from the standpoint that the metal complex is stable as compared with the peroxide but the intensification effect using such a metal complex is much lower than that using peroxide.
Furthermore, a disadvantage common to both attempts exists. That is, the above-described intensification attempts show hardly any intensification effect for color photographic materials for photography (i.e., highly sensitive color photographic materials using silver iodobromide containing more than about 2 mole percent silver iodide, generally more than 3 mole percent, for example 5 to 7 mole percent, silver iodide as the light-sensitive element. This is particularly marked in the intensification of color images using a cobalt (III) complex.
Example 1 of U.S. Pat. No. 3,748,138, described above, discloses that silver image densities can be intensified by processing a silver iodobromide photographic material containing 6 mole percent iodide in a black and white developer containing a cobalt (III) complex at 24.degree. C. Furthermore, Example 1 (amended) of Japanese Patent Application (OPI) No. 9728/1973 discloses that dye image densities are intensified by processing a silver iodobromide photographic material containing about 2 mole percent iodide in a color developer containing a cobalt (III) complex at 24.degree. C.
However, when attempts to follow the same disclosure on a silver iodobromide photographic material containing 2 mole percent iodide using the color developer having the same composition as above were made, no intensification effect was obtained.
Thus, since the intensification effect with the same cobalt (III) complex differs greatly depending on whether a black and white development or a color development is carried out, then it can be understood that the intensification technique obtained in a black and white development system will be inapplicable to a color development system.
It is quite incomprehensible that when a silver iodobromide color photographic material containing about 1 mole percent iodide is processed at temperatures of about 30.degree. C in the presence of a cobalt (III) complex, a color intensification effect is obtained (see, Example 10 of U.S. Pat. No. 3,765,891 described above), while when a silver iodobromide color photographic material containing a comparatively large amount of iodide, i.e., more than 2 mole percent iodide, is processed under the same condition as above, a color intensification effect is hardly obtained.
The mechanism of the color intensification using, in particular, a metal complex such as a cobalt (III) complex has not yet been clarified, and there has been no technique nor idea for achieving color intensification in processing a silver iodobromide color material containing more than about 2 mole percent iodide for photography and hence a solution to the above-described problem has been an important subject in the art.